The House's Stop Online Piracy Act (SOPA) and the Senate's Protect IP Act would empower the government and copyright holders to demand that search engines, Internet providers and ad networks block access to sites "dedicated" to copyright infringement.
The legislation is aimed at shutting down foreign sites such as The Pirate Bay that offer illegal copies of movies, music and television shows with impunity.
But tech companies such as Google are lobbying to kill the legislation, arguing it would impose unreasonable burdens on websites and could censor free speech.
They say that legitimate websites will have to monitor the content that users post to prevent the government from labeling them as "dedicated" to copyright infringement. They argue the legislation would stifle innovation online.
Supporters of the bills say they are only targeted at rogue websites and procedural protections will prevent legitimate websites from being blocked.
Wednesday's letter did not specifically mention SOPA or the Protect IP Act, but the companies did commend lawmakers "for their attention to this important issue."
"Not only are jobs and consumers at risk, but rogue sites contribute absolutely no value to the U.S. marketplace," they wrote. "The operators of rogue sites break laws, do not pay taxes, and skirt accountability. In light of these concerns, we urge you to enact carefully balanced rogue sites legislation this year."
--Updated at 5:34 p.m.